This invention relates to an emergency lighting system and, specifically, to a system for illuminating an exit, exit sign or other indication of a suitable escape route from a protected area under emergency conditions.
Almost everyone recognizes the familiar "EXIT" sign over the doors of buildings which lead to stairwells, corridors or the street. It is the essential and primary purpose of these exit signs to indicate to persons in the building exactly where the exit doors are so that under emergency conditions the exits can be located for quick evacuation of the premises. Indeed, almost every local safety code requires the provision of illuminated exit signs at all strategic locations.
Some local regulations require, in addition, that the emergency or exit lighting be provided with continuously available auxiliary power in the event of line power failure. This is to insure that the exit signs remain lighted even when a power failure occurs as a result of fire or electrical fault.
One such exit lighting system is found in U.S. Pat. No. 3,486,068. This system comprises a self-contained unit within the exit lighting fixture and includes a rechargeable battery and dual filament lamps normally supplied with alternating current line power through a transformer. Upon any loss of alternating current power, relays are operated to send battery current to the lamps to keep them illuminated. Conceivably, during an emergency condition causing loss of line power, persons would be able to find their way out, provided that the exit sign remains visible to them.
Another known system combines a standby auxiliary (battery) power feature with strategically placed heat detectors so as to provide normal exit lighting and a visual and audible alarm in the event that the temperature exceeds a predetermined limit indicating a fire or dangerous temperature condition. This system causes the incandescent lamps used to illuminate the exit sign to flash in order to better draw attention to the exit. The audible alarm is used to provide a warning in addition to helping persons locate the exit.
There are, in addition, a number of emergency lighting systems for general use which implement rechargeable batteries in order to maintain power to a lighting load in the event of power failure. In some of these systems, e.g., those disclosed in U.S. Pat. Nos. 3,819,980 and 3,771,012, electrical circuits are implemented which permit a lighting load to be continuously energized so long as the battery charge is sufficient. In one case, an electronic inverter is used to convert the DC battery power to AC power for the load. When the battery voltage falls below a predetermined level the inverter ceases to operate until such time as the battery recovers its charge. This results in a cyclical operation of the emergency lighting system and a blinking of the lights as the battery recovers and discarges. In another case, the battery power is supplied intermittently to the load in order to prolong bettery life and "attract attention to the power failure".
Unfortunately, none of the foregoing measures gives effective and reliable emergency lighting under what is perhaps one of the most common, and most deadly, of emergency conditions the smoke-filled room. Smokey fires are now commonplace, particularly with the proliferation of plastics and other similar materials which produce dense and acrid smoke when burning. The ordinary exit light often becomes inoperative due to loss of electrical power. Even if the emergency lighting or auxiliary power source is operating properly, the exits cannot be located because the illuminated exit indicators cannot be seen through the smoke. Although some smoke detector systems are available, e.g., that disclosed in U.S. Pat. No. 3,659,278, the system simply provides an alarm and does not help people to escape safely. In still other cases, the exit lights do not respond at all to either heat or smoke due to fires.
The shortcomings of systems now in use are dramatically underscored by all-too-common tragedies. In June of 1974, 24 young persons died from smoke inhalation caused by fire in a structure adjacent to a popular restaurant-discotheque. The kitchen of the establishment was equipped with a fire alarm system but the initial heat from the fire did not reach that area and did not set off the alarm. Smoke was present, but there were no smoke detectors in the building. Furthermore, the building was equipped with an emergency lighting system which had been tested by local authorities a few months earlier and were found to be operative. The building had six exits, all in working order and all marked with signs. Nevertheless, the thick smoke which permeated the room prevented the exit signs from being seen. This fact was a primary contributor to the shocking toll of lives in that incident in which all those who died could have escaped had they been able to find their way out.
In late 1975, seven persons died of smoke inhalation in a New York City nightclub after a fire, apparently electrical in origin, caused a power failure. Patrons and employees became hysterical because they could not find their way to an exit as dense smoke filled the room. Some persons who did escape were able to do so only by groping their way along walls until the street door was found. Those who died apparently mistook the washroom door as an escape route and there suffocated.
In each of these tragic incidences, the exits were maintained in accordance with fire code regulations and the casualties were the result of smoke inhalation and the inability to find the exit in darkness and smoke. In one of the cases, an emergency lighting system, assumed to have been operative, failed to direct the victims to a safe route of escape.
It is a principal object of the present invention to provide an emergency exit lighting system for directing those who may be trapped in a protected area to a safe route of escape under emergency conditions, including that of smoke, fire and power failures.
Another object of the invention is to provide a fail-safe exit lighting system which is inexpensive and reliable and suitable for installation in any public place, no matter what its size.
It is a general and overall object of the present invention to provide a system capable of preventing the tragic and needless loss of human lives due to inadequate emergency condition exit systems.